OK, I got the impression that you used a script to open the table.
Yes, it is possible to add data to the original table, but how to do it depends on wether the newly imported data is incremental (i.e. contains all data up to date) or only new data (to be added to the old data table).
One easy way is to concatenate the old table with the newly created table:
Activate the original table and choose Concatenate from the tables menu and select the new table in the list and add it to the "data tables to be concatenated" field. Make sure to select "Append to first table" before hitting OK.
If data is incremental, delete all rows from the original table before (or after) concatenating the tables to avoid duplicate records.
(Personally, when working interactively, I often simply copy the data in excel and paste into a new or existing JMP data table instead opening excel from within JMP)